For those products such as photosensitive material for use in color photographic paper that are used in such a field where a large amount of printed products has to be completed in a short time of delivery, silver chlorobromide containing substantially no silver iodide has been used in view of the necessity for increasing the developing speed.
The demand for the improvement of rapid processability of color photographic paper has greatly increased and various studies have been made in recent years in response thereto. It is well-known that the developing speed can be greatly improved by increasing the silver chloride content in the silver halide emulsion used.
Meanwhile, it is also well known that a technique of adding a sensitizing dye to a silver halide emulsion upon preparing a silver halide photographic material extends the region of light sensitive wavelength of the silver halide emulsion thereby optically sensitizing the same.
Various compounds are known as spectral sensitizing dyes used for such a purpose and there can be mentioned, for example, cyanine dyes, merocyanine dyes and xanthene dyes as described in "The Theory of the Photobraphic Process", third edition, p 198-228, edited by T. H. James, published by Macmillan Co. N.Y., 1966.
In the case of applying these sensitizing dyes to silver halide emulsions, it is usually necessary that they not only extend the region of light sensitive wavelength of the silver halide emulsion but also satisfy the following conditions:
(1) have a proper area of spectral sensitization, PA1 (2) have good sensitizing efficiency to obtain a sufficiently high sensitivity, PA1 (3) cause no fogging, PA1 (4) show less scattering of sensitivity due to the temperature change upon exposure, PA1 (5) have no undesirable interactions with other additives, for example, stabilizers, antifoggants, coating aids and color forming agents, PA1 (6) cause no sensitivity reduction when a silver halide emulsion containing the sensitizing dye is preserved, particularly under high temperature and high humidity conditions, and PA1 (7) do not diffuse to other photosensitive layers, which would lead to color turbidity (mixing of color).
The above-mentioned conditions are of critical importance, particularly, upon preparation of a red sensitive silver halide emulsion in a silver halide color photographic material.
However, in the case of using a so-called "high silver chloride emulsion containing a high content of silver chloride which has been increasingly demanded as described above, it is indeed difficult to obtain a red sensitizing dye capable of completely satisfying the above-mentioned conditions to the same extent as emulsions mainly composed of silver bromide. As the result of further specific study by the present inventors, it has been found that the variation in the sensitivity depending on the temperature change upon exposure, that is, the printing temperature dependency, is greatly increased in the case of using a high silver chloride emulsion as compared with using an emulsion mainly composed of silver bromide.
The correlation between the sensivitivity of spectral sensitization of a high silver chloride emulsion and the reduction potential of a spectral sensitizing dye therefor has been reported in "Photographic Science and Engineering", vol. 18, p 475-485 (1974) and "The Journal of Photographic Science", vol. 21, p 180-186 (1973). Further, to improve the spectral sensitivity, long term storage stability and anti-infrared fogging of a silver halide emulsion containing silver chloride spectrally sensitized with a specific red sensitizing dye, it has been proposed to add a nitrogen-containing compound as disclosed in JP-B No. 46-10473 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-B No. 48-42494, a supersensitizer as disclosed in JP-A No. 50-5035 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), a water-soluble bromide as disclosed in JP-A No. 52-151026, iridium as disclosed in JP-A No. 54-23520 and a film hardener as disclosed in JP-A No. 60 202436. It has also been proposed in JP-A No. 58-7629 to improve the addition method of spectral sensitizing dye and, further, to use silver chlorobromide having a (100) face and a (111) face as disclosed in JP-A No. 60-225147.
However, although the printing temperature dependency is remarkably worsened by the use of the silver chloride emulsion as compared with the emulsion mainly composed of silver bromide, the above-mentioned publications disclose nothing in terms of a technique of improving the printing temperature dependency by reducing the variation in sensitivity depending on the temperature change upon exposure. In addition, improvement in the long term storage stability has also been insufficient by the known methods. In view of the above, a high silver chloride photographic material exhibiting no variation in sensitivity depending on the temperature change upon exposure and having excellent long term storage stability has been desired.